This invention relates generally to therapeutic spas and hot tubs and the like. More specifically, this invention relates to improvements in a spa control circuit for regulating a water circulation and heating system, wherein the circulation/heating system provides jets of heated water to a spa interior.
Spas and hot tubs are generally known in the art for relaxation and other therapeutic purposes. In general terms, the spa or hot tub comprises an upwardly open tub structure for receiving and storing a supply of water, wherein the tub structure has a size and shape sufficient for substantial immersion of one or more persons. A water circulation and heating system is normally provided, to include a pump for circulating water from the spa interior through a filter and a heater, and for return flow to the spa. The filtered and heated water is normally returned to the spa in the form of a plurality of pressurized water jets, often including entrained air, wherein these jets provide a vigorous and therapeutic massage action.
The water circulation and heating system for the spa or hot tub commonly includes a control circuit for regulating water temperature and to prevent overheating. More specifically, in a typical spa control circuit, a thermostat circuit responds to actual water temperature as detected by a temperature sensor to cycle the system heater between on-off states for purposes of maintaining the water temperature within a predetermined range, such as between about 100 to 110 degrees Fahrenheit. In addition, the control circuit commonly includes a high temperature limit circuit which responds to a separate temperature sensor to deactivate the heater when an upper end limit temperature limit is reached, such as about 120 degrees Fahrenheit.
One preferred spa construction is shown and described in U.S. Pat. Nos. 4,843,659; 4,858,254; 4,981,543; 5,092,951; and 5,133,818, which are incorporated by reference herein. In accordance with this spa design, a relatively lightweight tub structure is formed from insulative foam plastic walls. The water circulation and heating system comprises a motor-driven pump for drawing spa water through a filter and for returning the filtered water in the form of jets to the spa interior. A portion of the circulated water is passed in heat transfer relation with the pump motor, whereby the pump motor comprises the heat source for elevating the temperature of the spa water. A thermostat circuit and a high temperature limit circuit are respectively provided for regulating water temperature within a normal operational range, and to prevent water overheating.
While the above-referenced spa construction beneficially provides a cost-efficient and energy-efficient system, certain failure mode conditions can occur to result in undesired operation, such as inadvertent overheating of the spa water. For example, temperature sensor failure can be interpreted by the control circuit as a drop in water temperature, thereby incorrectly signaling the control circuit to operate the circulation/heating system in a manner elevating the water temperature above acceptable limits. As another example, repeated on-off cycling of the thermostat circuit can result in arc damage of relay contacts used to connect and disconnect a power supply to the pump motor.
The present invention overcomes these and other problems encountered in the prior art by providing an improved control circuit for use with a spa or hot tub or the like, wherein the control circuit includes safety features to prevent water overheating as a result of control circuit component failure. The improved control circuit also includes arc suppression means to protect relay contacts from damage due to arcing.